1. Field of the Invention
The present invention relates to a redundantly constructed PCA (Protection Channel Access) transmission apparatus having current units and spare units and a PCA transmission method, and more specifically, to a PCA transmission apparatus for and a PCA transmission method of transmitting other information by making use of spare units.
2. Description of the Related Art
During a redundantly constructed transmission apparatus is operated through current units, spare units are not used at all and thus there is a requirement that the spare units must be utilized effectively. Therefore, a PCA system is employed to transmit other information by making use of the spare units.
FIG. 1 is a block diagram showing the construction of a conventional transmission apparatus. There is, for example, a transmission apparatus for SONET (Synchronous Optical NETwork) as an example of this kind of the transmission apparatus. This transmission apparatus is composed of current units 91a-91n, spare units 92a-92n, a current high speed channel unit 100 and a spare high speed channel unit 110. The transmission apparatus also includes a control unit 80 composed of a microprocessor for monitoring and controlling these respective units. Although the control unit 80 is interconnected with the other units through an interface (microcomputer interface), respectively, these connections are not shown in FIG. 1.
First, data DS1-DSn of DS-3 format are input to the current units 91a-91n and the spare units 92a-92n and converted into signals of STS-1X3 format.
The control unit 80 monitors whether or not the current units 91a-91n and the spare units 92a-92n are in an alarm state, and when the current units 91a-91n are in a normal state, the outputs of the spare units 92a-92n are made to a high impedance state and separated.
Then, the data DS1-DSn are multiplied by the multiplying unit 101 of the current high speed channel unit 100 and further converted into optical signals and output.
Conversely, when the current unit 91a fails and is in an alarm state, the control unit 80 is aware of this state through the interface and makes the output of the current unit 91a to a high impedance state and separates the same and returns the output of the spare unit 92a from a high impedance state to a usual output. With this arrangement, the spare unit 92a is used in place of the current unit 91a.
Further, when the current high speed channel unit 100 fails and is made to an alarm state, it may be switched to the spare high speed channel unit 110.
In this transmission apparatus, however, when the current units 91a-91n are in a normal state, the spare units 92a-92n are not used at all and they are wasted.
Therefore, the PCA transmission apparatus is used to transmit other information using the spare units 92a-92n in order to effectively utilize them.
In the PCA transmission apparatus, however, when any one of the current units is in an alarm state and one of the spare units corresponding to it is used, a problem arises in that PCA data cannot be transmitted.